Ethylene-based copolymers and their use as flow improvers in mineral oil middle distillates

ABSTRACT

Ethylene-based copolymers which are suitable as flow improvers for mineral oil middle distillates are composed of 
     a) from 50 to 94% by weight of ethylene, 
     b) from 3 to 30% by weight of one or more vinyl esters of C 2  -C 6  -monocarboxylic acids, 
     c) from 3 to 20% by weight of one or more aminoalkyl acrylates of the general formula I ##STR1##  where R 1  is hydrogen or methyl, R 2  and R 3  may be identical or different and are each hydrogen or C 1  -C 6  -alkyl and A 1  is straight-chain or branched C 2  -C 10  -alkylene, and 
     d) from 0 to 10% by weight of one or more monomers which are copolymerizable with the monomers a) to c), 
     copolymers in which monomer b) is vinyl acetate and which have a number average molecular weight of from 5000 to 50,000 being excluded, or are composed of 
     a&#39;) from 50 to 95.5% by weight of ethylene, 
     b&#39;) from 4 to 30% by weight of one or more vinyl esters of C 2  -C 6  -monocarboxylic acids, 
     c&#39;) from 0.5 to 20% by weight of one or more vinylimidazoles of the general formula II ##STR2##  where R 4 , R 5  and R 6  may be identical or different and are each hydrogen or C 1  -C 6  -alkyl, or 
     from 0.5 to 20% by weight of one or more aminoalkyl vinyl ethers of the general formula III 
     
         R.sup.7 R.sup.8 N--A.sup.2 --O--CR.sup.9 ═CR.sup.10 R.sup.11(III) 
    
     where 
     R 7  and R 8  are each C 1  -C 6  -alkyl, 
     R 9 , R 10  and R 11  are each hydrogen or C 1  -C 6  -alkyl and 
     A 2  is C 2  -C 6  -alkylene, and 
     d&#39;) from 0 to 10% by weight of one or more monomers which are copolymerizable with the monomers a&#39;) to c&#39;).

This is a Division of application Ser. No. 08/615,175 filed on Apr. 2,1996, now U.S. Pat. No. 5,684,108, which was filed as InternationalApplication No. PCT/EP94/03179 filed on Sep. 23, 1994.

The present invention relates to novel ethylene-based copolymers, theuse of these and of copolymers known per se as flow improvers in mineraloil middle distillates, and furthermore mineral oil middle distillateswhich contain these copolymers.

Middle distillates, such as gas oils, diesel oils or fuel oils, whichare obtained from mineral oils by distillation, have different contentsof paraffins, depending on the origin of the crude oil. At relativelylow temperatures, solid paraffins separate out (cloud point, CP). Onfurther cooling, the lamellar n-paraffin crystals form a house-of-cardsstructure, and the middle distillate sets although the predominant partof the middle distillate is still liquid. The flow of the fuels obtainedfrom the mineral oil distillate is considerably impaired by theprecipitated n-paraffins in the temperature range between cloud pointand pour point. The paraffins block filters and cause nonuniform fuelfeed to the combustion units or completely stop the feed. Similarproblems occur in the case of fuel oils.

It has long been known that the crystal growth of the paraffins in thecombustion and power fuels obtained from the mineral oil middledistillates can be modified by means of suitable additives. Effectiveadditives on the one hand prevent middle distillates from forming suchhouse-of-cards structures and becoming solid at temperatures as low as afew degrees Celsius below the temperature at which the first paraffincrystals crystallize out and, on the other hand, form fine,well-crystallized, separate paraffin crystals which pass through filtersin motor vehicles and heating systems or at least form a filter cakewhich is permeable to the liquid part of the middle distillates, thusensuring trouble-free operation.

Ethylene/vinyl carboxylate copolymers as disclosed, for example, in U.S.Pat. No. 3,048,479 and U.S. Pat. No. 3,627,838 have long been used asflow improvers.

A disadvantage of these additives is that, because they have a higherdensity than the liquid part, the precipitated paraffin crystals tendincreasingly to settle out on the bottom of the container duringstorage. Consequently, a homogeneous phase having a low paraffin contentforms in the upper part of the container and a two-phase paraffin-richlayer at the bottom. Since, both in vehicle tanks and in the mineral oildealers' storage or delivery tanks, the middle distillate is generallywithdrawn slightly above the bottom of the container, there is a dangerthat the high concentration of solid paraffins will lead to blockages offilters and metering means. This danger is all the greater the furtherthe storage temperature is below the precipitation temperature of theparaffins, since the amount of paraffin precipitated is a function ofthe temperature and increases with decreasing temperature.

JP-A 83/80386 describes flow improvers comprising ethylene, vinylacetate and N-vinyl-2-pyrrolidone, which however do not givesatisfactory results in all cases in practice since the mineral oilfractions to be treated differ greatly in composition, depending ontheir origin. According to EP-A 405 270, the action of the terpolymersdisclosed in the Japanese patent application can be improved by mixingwith an ethylene/vinyl acetate copolymer; on the other hand, theaddition of a plurality of polymers to the mineral oil middledistillates is technically very complicated.

U.S. Pat. No. 2,787,459 discloses copolymers made from monomers whichcarry a basic nitrogen atom, such as aminoalkyl acrylates, and thosemonomers which carry no amino group but a hydrocarbon radical of 8 to 18carbon atoms. They are used for dispersing sludge, as may be obtainedfrom fuel oils.

EP-A 340 975 describes copolymers of ethylene and aminoalkyl acrylates,which may contain up to 20% by weight of vinyl acetate and have a numberaverage molecular weight of from 5000 to 50,000. The copolymers are usedfor reducing the concentration of metal ions in aqueous solution.

It is an object of the present invention to provide copolymers whichensure the flow of mineral oil middle distillates at low temperature andwhich have a dispersing effect such that settling out of precipitatedparaffins is delayed or prevented. The flow improvers should displaytheir action independently of the composition of the mineral oil middledistillates.

We have found that this object is achieved by ethylene-based copolymerswhich are composed of

a) from 50 to 94% by weight of ethylene,

b) from 3 to 30% by weight of one or more vinyl esters of C₂ -C₆-monocarboxylic acids,

c) from 3 to 20% by weight of one or more aminoalkyl acrylates of thegeneral formula I ##STR3## where R¹ is hydrogen or methyl, R² and R³ maybe identical or different and are each hydrogen or C₁ -C₆ -alkyl and A¹is straight-chain or branched C₂ -C₁₀ -alkylene, and

d) from 0 to 10% by weight of one or more monomers which arecopolymerizable with the monomers a) to c),

copolymers in which monomer b) is vinyl acetate and which have a numberaverage molecular weight of from 5000 to 50,000 being excluded, or arecomposed of

a') from 50 to 95.5% by weight of ethylene,

b') from 4 to 30% by weight of one or more vinyl esters of C₂ -C₆-monocarboxylic acids,

c') from 0.5 to 20% by weight of one or more vinylimidazoles of thegeneral formula II ##STR4## where R⁴, R⁵ and R⁶ may be identical ordifferent and are each hydrogen or C₁ -C₆ -alkyl, or

from 0.5 to 20% by weight of one or more aminoalkyl vinyl ethers of thegeneral formula III

    R.sup.7 R.sup.8 N--A.sup.2 --O--CR.sup.9 ═CR.sup.10 R.sup.11(III)

where

R⁷ and R⁸ are each C₁ -C₆ -alkyl,

R⁹, R¹⁰ and R¹¹ are each hydrogen or C₁ -C₆ -alkyl and

A² is C₂ -C₆ -alkylene, and

d') from 0 to 10% by weight of one or more monomers which arecopolymerizable with the monomers a') to c').

The abovementioned number average is determined by measuring theviscosity (cf. EP-A 340 975).

We have also found the use of the stated copolymers as additives formineral oil middle distillates, and mineral oil middle distillates whichcontain these copolymers.

The novel copolymers have, as a rule, a weight average molecular weightof from 300 to 8000, and, in view of their use as flow improvers, thosehaving a molecular weight of from 500 to 5000, especially from 1000 to3000, are preferred. The molecular weight is determined by gelpermeation chromatography. The novel copolymers generally have aviscosity of from 1000 to 2000, preferably from 250 to 1000, mm² /s,determined according to DIN 53 019 at 120° C.

The copolymers are composed of at least three monomers:

a) in the case of aminoalkyl acrylates I as monomers c), the amount ofethylene is preferably from 50 to 92, in particular from 65 to 87, % byweight, or

a') in the case of vinylimidazoles II or aminoalkyl vinyl ethers III asmonomers c'), the amount of ethylene is preferably from 65 to 94% byweight.

b) Preferred components b) are vinyl acetate and vinyl propionate andmixtures thereof, or compounds such as vinyl butyrate. Preferably, theamount of monomers b) is from 5 to 30, in particular from 10 to 23, % byweight in the case of aminoalkyl acrylates I as monomers c), and from 4to 23% by weight in the case of vinylimidazoles II or aminoalkyl vinylethers III as monomers c').

c) Monomer c) of the general formula I comprises aminoalkyl acrylatesand methacrylates. Examples of alkyl radicals A¹ are ethylene,n-propylene, n-butylene, dimethylethylene and sec-butylene.

R² and R³ may be, for example, hydrogen, methyl, ethyl, n-propyl,isobutyl and n-butyl, among which methyl is preferred. Examples ofsuitable monomers c) are aminoethyl acrylate, amino-n-butyl acrylate,N-methylaminoethyl acrylate, N,N-di-n-butylamino-n-propyl acrylate andthe corresponding methacrylates, dimethylaminoethyl acrylate anddimethylaminoethyl methacrylate being preferred.

The monomers are commercially available or can be prepared by knownmethods, for example by esterifying acrylates with aminoalcohols in thepresence of a titanium catalyst (cf. EP-A 188 639).

The preferred amount of aminoalkyl acrylates I as monomers c) is from 3to 12% by weight.

c') Monomer c') of the general formula II comprises vinylimidazoles.

R⁴, R⁵ and R⁶ may be, for example, hydrogen, methyl, ethyl, n-propyl,isopropyl and n-butyl, among which hydrogen is preferred. Examples ofsuitable monomers c') are 2-methylvinylimidazole, 4-methylvinylimidazoleand 5-methylvinylimidazole, the parent structure vinylimidazole beingpreferred.

The monomers are commercially available or can be prepared by knownmethods.

The preferred amount of vinylimidazoles II as monomers c') is from 1 to4% by weight.

Monomer c') of the general formula III comprises aminoalkyl vinylethers.

R⁷, R⁸, R⁹, R¹⁰ and R¹¹ may be identical or different and are each C₁-C₆ -alkyl, e.g. methyl, ethyl, n-propyl, isopropyl and n-butyl. R⁹, R¹⁰and R¹¹ may furthermore be hydrogen. The C₂ -C₆ -alkylene radical A² isstraight-chain or branched alkylene, for example ethylene, n-propylene,dimethylmethylene, methylethylmethylene and dimethylethylene. Preferredcompounds are those in which R⁷ and R⁸ are identical and are each C₁ -C₃-alkyl, A² is a straight-chain C₂ -C₄ -radical and R⁹, R¹⁰ and R¹¹ areeach hydrogen, as in diethylaminoethyl vinyl ether anddimethylaminopropyl vinyl ether.

These monomers are obtainable, for example, according to Liebigs Ann.Chem. 601 (1956), 81.

The preferred amount of aminoalkyl vinyl ethers III as monomers c') isfrom 0.5 to 5% by weight.

d) Suitable monomers d) and d') are monomers which are copolymerizablewith components a) to c), and a') to c'), respectively, and which mayreplace these without substantially influencing the properties of thecopolymers, e.g. propene. The amount of monomer d) or d') is preferablyfrom 0 to 2% by weight.

The copolymers are prepared in a manner known per se by polymerizing themonomers a) to d) or a') to d'). The vinylimidazole II or the aminoalkylvinyl ether III is incorporated in preference to ethylene, so that thecontent of said vinylimidazole or of said aminoalkyl vinyl ether in thenovel copolymers is increased compared with the starting monomermixture. In a preferred embodiment, the monomers are polymerized in theabsence of a solvent at from 50 to 400, preferably from 100 to 300, MPaand at from 150° to 350° C., preferably from 180° to 280° C., in thepresence of compounds which form free radicals. The average residencetime is in general from 60 to 120 seconds. Examples of suitable freeradical initiators are peroxides, such as di-tert-butyl peroxide,tert-butyl peroxypivalate or tert-butyl peroxy-3,5,5-trimethylhexanoate,the amount of which is as a rule less than 5% by weight, based on themonomers used in the course of polymerization. In order to prepare lowmolecular weight copolymers, it is often advantageous to carry out thecopolymerization in the presence of regulators, such as C₁ -C₄-aldehydes, e.g. propionaldehyde, or organic SH-containing compounds,the amount of which is in general from 0.1 to 5% by weight, based on thesum of the monomers. The polymerization can be carried out, for example,in an autoclave, a tube reactor or a combination of tube reactor andautoclave.

The novel copolymers are used as additives for mineral oil middledistillates, which are understood as meaning petroleum, fuel oil anddiesel fuels having a boiling point of from about 150° to 400° C. Thecopolymers may be added to the middle distillates directly or,preferably, as a 20-70% strength by weight solution. Suitable solventsare aliphatic or aromatic solvents, such as xylene or mixtures thereof,as well as high-boiling mixtures of aromatics, and middle distillates.The amount of copolymers in the mineral oil middle distillates is as arule from 10 to 10,000, preferably from 50 to 5000, ppm. Depending onthe intended use, the middle distillates may contain further additives,such as flow improvers, dispersants, antifoams, corrosion inhibitors,antioxidants, conductivity improvers and dyes.

Regardless of their origin, the copolymers result in a substantialimprovement in the low-temperature flow properties in middledistillates. In addition, they keep precipitated paraffin crystalseffectively in suspension, so that there is no blockage of filters andlines by paraffin which has settled out.

EXAMPLES

1. General Preparation Method I

Ethylene, vinyl propionate or acetate and dimethylaminoethyl acrylate orvinylimidazole are polymerized in an autoclave, with the addition ofpropionaldehyde as a regulator. The free radical initiation of thepolymerization was carried out by continuously metering in anisododecane solution which contained 0.2% by weight of tert-butylperoxypivalate and 0.5% by weight of tert-butylperoxy-3,5,5-trimethylhexanoate. The autoclave had an internal volume of1l and a length/diameter ratio of 5:1. The average residence time of thereaction mixture in the autoclave was about 90 seconds.

The polymerization conditions and the ratios of the monomers are listedin Tables 1 and 2 below.

Table 3 shows the composition of the copolymers prepared by the abovemethod with the concomitant use of vinylimidazole.

                                      TABLE 1                                     __________________________________________________________________________    Example No.                                                                         Reaction                                                                           Reaction                                                                            Composition of the reaction                                                                        Free                                    according to                                                                        pressure                                                                           temperature                                                                         reaction mixture.sup.a)                                                                            radical                                 the invention                                                                        MPa!                                                                               °C.!                                                                        C.sub.2 H.sub.4                                                                  VPr.sup.d)                                                                       VAc.sup.e)                                                                        DMAEA.sup.f)                                                                       DMAEMA.sup.g)                                                                       initiator.sup.b)                                                                   Regulator.sup.c)                   __________________________________________________________________________    1     150  250   85.6                                                                             10.2                                                                             --  4.2  --    13.7 2.1                                2     150  250   85.8                                                                             10.0                                                                             --  4.2  --    10.6 1.29                               3     150  235   75.0                                                                             18.2                                                                             --  6.8  --    19.1 0.80                               4     150  250   79.0                                                                             -- 15.4                                                                              5.6  --    9.4  1.78                               5     150  235   80.5                                                                             13.2                                                                             --  5.9  --    13.3 0.43                               6     150  235   80.1                                                                             13.6                                                                             --  6.3  --    8.3  1.23                               7     150  250   75.8                                                                             19.0                                                                             --  5.2  --    22.7 1.06                               8     150  250   73.5                                                                             22.1                                                                             --  4.4  --    19.7 0.30                               9     150  230   94.0                                                                             -- 3.0 --   3.2   12.2 0.42                               10    150  230   88.2                                                                             -- 4.1 --   7.7   14.1 0.59                               11    150  230   91.9                                                                             -- 4.9 --   3.2   13.2 0.51                               12    150  230   90.5                                                                             -- 6.5 --   3.0   13.9 0.72                               13    150  235   75.9                                                                             16.9                                                                             --  --   7.2   18.3 0.80                               Comparison                                                                          150  250   93.7                                                                             -- --  6.3  2.3   8.1  2.3                                V 1                                                                           V 2   150  250   94.0                                                                             -- --  6.0  1.8   13.4 1.8                                V 3   190  200   68.9                                                                             -- 11.1                                                                              --   2.1   0.96 2.1                                __________________________________________________________________________     .sup.a) % by weight, based on the reaction mixture                            .sup.b) ppm by weight, based on ethylene                                      .sup.c) % by weight, based on monomers                                        .sup.d) VPr = vinyl propionate                                                .sup.e) VAc = vinyl acetate                                                   .sup.f) DMAEA = dimethylaminoethyl acrylate                                   .sup.g) DMAEMA = dimethylaminoethyl methacrylate                         

                                      TABLE 2                                     __________________________________________________________________________    Example No.                                                                         Reaction                                                                           Reaction                                                                            Composition of the                                           according to                                                                        pressure                                                                           temperature                                                                         reaction mixture.sup.a)                                                                    Free radical                                    the invention                                                                        MPa!                                                                               °C.!                                                                        C.sub.2 H.sub.4                                                                  VPr.sup.d)                                                                       VAc.sup.e)                                                                        VI.sup.f)                                                                        initiator.sup.b)                                                                    Regulator.sup.c)                          __________________________________________________________________________    14    150  236   93.2                                                                             6.1                                                                              --  0.8                                                                              33.1  2.8                                       15    150  234   93.5                                                                             5.8                                                                              --  0.7                                                                              6.5   2.9                                       16    151  231   90.9                                                                             8.4                                                                              --  0.7                                                                              17.7  3.1                                       17    151  235   87.9                                                                             11.4                                                                             --  0.7                                                                              23.8  3.1                                       18    150  232   85.9                                                                             13.5                                                                             --  0.6                                                                              27.4  2.7                                       19    151  235   88.3                                                                             10.4                                                                             --  1.3                                                                              24.5  2.8                                       20    151  234   94.1  5.2 0.7                                                                              4.7   2.9                                       21    149  234   66.9                                                                             29.4                                                                             --  3.7                                                                              193.3 0.9                                       22    151  236   73.9                                                                             23.2                                                                             --  2.9                                                                              139.4 1.2                                       23    150  234   83.8                                                                             14.4                                                                             --  1.8                                                                              32.9  2.9                                       Comparison                                                                          190  200   88.9                                                                             -- 11.1                                                                              -- 1.0   2.1                                       V 4                                                                           __________________________________________________________________________     .sup.a) % by weight, based on reaction mixture                                .sup.b) ppm by weight, based on ethylene                                      .sup.c) % by weight, based on monomers                                        .sup.d) VPr = vinyl propionate                                                .sup.e) VAc = vinyl acetate                                                   .sup.f) VI = vinylimidazole                                              

                  TABLE 3                                                         ______________________________________                                        Composition of the copolymers                                                 Example No.                                                                           C.sub.2 H.sub.4                                                                        VPr     VAc    VI                                            according to                                                                           % by     % by    % by   % by Viscosity*.sup.)                        the invention                                                                         weight!  weight! weight!                                                                              weight!                                                                              mm.sup.2 /s!                           ______________________________________                                        14      76.5     22.1    --     1.4    460                                    15      93.9     4.7     --     1.4    420                                    16      91.7     6.9     --     1.4    250                                    17      89.9     6.8     --     1.3    250                                    18      86.9     12.0    --     1.1    240                                    19      88.9     8.6     --     2.5    230                                    20      92.9     --      5.7    1.4    240                                    21      68.1     24.9    --     7.0    460                                    22      75.3     1.3     --     5.4    480                                    23      85.9     10.6    --     3.5    250                                    Comparison                                                                            88.9     --      11.1   --     280                                    V 4                                                                           ______________________________________                                         *.sup.) in the rotary viscometer according to DIN 53 019 at 120°       C.; vinylimidazole is more readily incorporated into the copolymer than i     ethylene                                                                 

2. General Preparation Method II

Ethylene, vinyl propionate or acetate and diethylaminoethyl vinyl etherwere polymerized in an autoclave, with the addition of propionaldehydeas regulator. The free radical initiation of the polymerization wascarried out at 235° C. and 150 MPa by continuously metering in anisododecane solution which contains 0.2% by tert-butyl peroxypivalateand 0.5% by weight of tert-butyl peroxy-3,5,5-trimethylhexanoate. Theautoclave had an internal volume of 1l and a length/diameter ratio of5:1. The average residence time of the reaction mixture in the autoclave90 seconds.

The polymerization conditions and the ratios of the monomers in thereaction mixture are listed in Table 4 below. Table 5 shows thecomposition of the copolymers prepared by the above method.

                  TABLE 4                                                         ______________________________________                                        Example No.                                                                           Composition of the                                                    according to                                                                          reaction mixture.sup.a)                                                                        Free radical                                         the invention                                                                         C.sub.2 H.sub.4                                                                      VPr.sup.d)                                                                            DEAEVE.sup.e)                                                                         initiator.sup.b)                                                                      Regulator.sup.c)                       ______________________________________                                        24      93.7   5.7     0.6     1.8     2.7                                    25      83.4   15.0    1.6     9.9     1.9                                    26      74.6   23.0    2.4     32.6    0.4                                    27      86.6   7.8     3.6     6.9     2.0                                    28      82.5   10.9    5.0     10.6    1.7                                    29      78.7   13.9    6.3     18.6    1.1                                    30      75.4   16.3    7.4     18.9    0.9                                    31      72.2   18.8    8.6     42.5    0.4                                    Comparison                                                                            78.8   21.2    --      2.0     1.9                                    V 5                                                                           ______________________________________                                         .sup.a) % by weight, based on reaction mixture                                .sup.b) ppm by weight, based on ethylene                                      .sup.c) % by weight, based on monomers                                        .sup.d) VPr = vinyl propionate                                                .sup.e) DEAEVE = diethylaminoethyl vinyl ether                           

                  TABLE 5                                                         ______________________________________                                        Composition of the copolymers                                                 Example No.                                                                             C.sub.2 H.sub.4                                                                       VPr       DEAEVE                                            according to                                                                             % by    % by      % by  Viscosity*.sup.)                           invention weight! weight!   weight!                                                                               mm.sup.2 /s!                              ______________________________________                                        24        94.4    5.1       0.5    450                                        25        87.0    12.0      1.0    480                                        26        84.9    13.6      1.5    400                                        27        93.1    5.1       1.8    460                                        28        89.3    8.1       2.6    410                                        29        86.5    10.0      3.4    420                                        30        82.6    13.3      4.1    410                                        31        79.3    16.0      4.7    390                                        Comparison                                                                              86.8    13.2      --     460                                        V 5                                                                           ______________________________________                                         *.sup.) in the rotary viscometer according to DIN 53 019 at 120°       C.; DEAEVE is more readily incorporated into the copolymer than is            ethylene.                                                                

3. Use Examples

The novel copolymers and the comparative compounds were tested in anumber of middle distillates. These are diesel fuels of commercialGerman refinery quality; they are referred to as DK 1 to DK 7:

    ______________________________________                                               DK 1 DK 2    DK 3   DK 4  DK 5 DK 6  DK 7                              ______________________________________                                        Cloud point                                                                            -8     -7      -4   -7    -8   -7    -7                              (°C.)                                                                  CFPP (°C.)                                                                      -12    -10     -7   -14   -10  -9    -9                              Density at                                                                             0.831  0.829   0.832                                                                              0.814 0.831                                                                              0.831 0.826                           20° C. (g/ml)                                                          Initial  175    183     171  164   175  172   172                             boiling point                                                                 (°C.)                                                                  20% boiling                                                                            223    211     220  206   223  216   217                             point (°C.)                                                            90% boiling                                                                            314    317     332  306   314  325   321                             point (°C.)                                                            Final boiling                                                                          352    364     363  337   352  343   356                             point (°C.)                                                            ______________________________________                                    

3.1 Description of the Test Methods

The appropriate amounts of the novel examples 1 to 31 and ComparativeExamples V1 to V5 (50% strength in Solvesso® 150, a high-boilingaromatic hydrocarbon mixture from Esso) were added to the middledistillates at 40° C. with stirring, and the mixture was then cooled toroom temperature.

Test 1

The middle distillates containing the additive were stored in 100 mlmeasuring cylinders for 20 hours in a refrigerator at -13° C. The volumeand appearance of the paraffin phase which had settled out and the oilphase above this were then determined and evaluated visually. Inaddition, the cold filter plugging point (CFPP) of each sample wasmeasured according to DIN EN 116.

The results are shown in Tables 6 to 14. It is evident that the novelcopolymers 1 to 31 have not only a good CFPP-improving effect but alsoan excellent effect as paraffin dispersants. In contrast, thecomonomeric Comparative Examples V1 and V2 based on ethylene/aminoacrylate lead only to an insufficient improvement in the CFPP, andExample V3 based on ethylene/vinyl propionate is ineffective as paraffindispersant. Comparative Example V4 based on ethylene/vinyl acetate leadsonly to an insufficient paraffin-dispersing effect. Comparative ExampleV5, too, does not lead to sufficient dispersing of the paraffins.

                  TABLE 6                                                         ______________________________________                                        Dispersing tests (Test 1) in DK 1, CP: -8° C., CFPP: 12°        C.                                                                                       Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        1     300     -24    95    dispersed                                                                             5     clear                                2     300     -23    95    dispersed                                                                             5     clear                                3     300     -22    100   dispersed                                                                             0     --                                   4     300     -24    90    dispersed                                                                             10    clear                                5     300     -26    85    dispersed                                                                             15    clear                                6     300     -25    100   dispersed                                                                             0     --                                   7     300     -29    90    dispersed                                                                             10    clear                                8     300     -25    85    dispersed                                                                             15    clear                                Comp. 300     -17    100   dispersed                                                                             0     --                                   V1                                                                            V2    300     -18    100   dispersed                                                                             0     --                                   V3    300     -25    55    flocculent                                                                            45    clear                                ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Dispersing tests (Test 1) in DK2, CP: -7° C., CFPP: -10°        C.                                                                                       Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        2     300     -23     80   dispersed                                                                             20    clear                                5     300     -26    100   dispersed                                                                              0    --                                   6     300     -25    100   dispersed                                                                              0    --                                   8     300     -25    80    dispersed                                                                             20    clear                                ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Dispersing tests (Test 1) in DK 3, CP: -4° C., CFPP: 7° C.                 Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        1     300     -18    95    dispersed                                                                             5     clear                                2     300     -17    100   dispersed                                                                             0     --                                   4     300     -19     95   dispersed                                                                             5     clear                                5     300     -19    100   dispersed                                                                             0     --                                   6     300     -18     95   dispersed                                                                             5     clear                                9     300     -17    100   dispersed                                                                             0     --                                   10    300     -18     95   dispersed                                                                             5     clear                                11    300     -18    100   dispersed                                                                             0     --                                   12    300     -19    100   dispersed                                                                             0     --                                   13    300     -17    100   dispersed                                                                             0     --                                   Comp. 300     -19     30   flocculent                                                                            70    clear                                V3                                                                            ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Dispersing tests in DK 5, CP: -8° C., CFPP: -10° C.                        Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        14    300     -24    90    dispersed                                                                             10    clear                                15    300     -19    85    dispersed                                                                             15    clear                                16    300     -24    80    dispersed                                                                             20    cloudy                               17    300     -22    95    dispersed                                                                              5    clear                                18    300     -25    70    dispersed                                                                             30    clear                                19    300     -20    80    dispersed                                                                             20    cloudy                               20    300     -24    100   dispersed                                                                              0    --                                   Comp. 300     -25    55    flocculent                                                                            45    clear                                V4                                                                            ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Dispersing tests in DK 6, CP: -7° C., CFPP: -9° C.                         Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        15    300     -14    100   dispersed                                                                             0     --                                   16    300     -13    100   dispersed                                                                             0     --                                   17    300     -14    100   dispersed                                                                             0     --                                   18    300     -14    100   dispersed                                                                             0     --                                   19    300     -14    100   dispersed                                                                             0     --                                   20    300     -13    100   dispersed                                                                             0     --                                   Comp. 300     -19     30   flocculent                                                                            70    clear                                V4                                                                            ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Dispersing tests DK 7, CP: -7° C., CFPP: -9° C.                            Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        14    300     -14    100   dispersed                                                                             0     --                                   15    300     -12    100   dispersed                                                                             0     --                                   16    300     -13    100   dispersed                                                                             0     --                                   17    300     -13    100   dispersed                                                                             0     --                                   18    300     -13     90   dispersed                                                                             10    clear                                19    300     -12    100   dispersed                                                                             0     --                                   20    300     -13    100   dispersed                                                                             0     --                                   ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                        Dispersing tests in DK 5, CP: -8° C., CFPP: -10° C.                        Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        24    300     -18    90    dispersed                                                                             10    clear                                27    300     -20    97    dispersed                                                                              3    clear                                28    300     -20    85    dispersed                                                                             15    clear                                29    300     -24    90    dispersed                                                                             10    clear                                30    300     -25    90    dispersed                                                                             10    clear                                31    300     -26    95    dispersed                                                                              5    clear                                Comp. 300     -25    55    flocculent                                                                            45    clear                                V5                                                                            ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                        Dispersing tests in DK 2, CP: -7° C., CFPP: -10° C.                        Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        25    300     -20    70    dispersed                                                                             30    clear                                26    300     -27    70    dispersed                                                                             30    clear                                ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        Dispersing tests in DK 7, CP: -7° C., CFPP: -9° C.                         Paraffin phase                                                                            Oil phase                                                    Dose    CFPP   (%            (%                                         Ex.   (ppm)   (°C.)                                                                         by vol.)                                                                            Appearance                                                                            by vol.)                                                                            Appearance                           ______________________________________                                        24    300     -12    100   dispersed                                                                              0    --                                   25    300     -12     75   dispersed                                                                             25    clear                                ______________________________________                                    

Test 2

The additive-containing middle distillates were cooled in 500 ml glasscylinders in a cold bath from room temperature to -18° C. and stored for20 hours at this temperature. The amount and appearance of the paraffinphase were then determined and evaluated visually. The cold filterplugging point (CFPP) of each sample of the 20% by volume of bottomphase separated off at -18° C. was determined according to DIN EN 116and the cloud point (CP) according to ASTM D 2500.

                  TABLE 15                                                        ______________________________________                                        Dispersing tests (Test 2) in DK 4, CP: -7 ° C., CFPP: -14°      C.                                                                                                  20% bottom phase                                        Dose     CFPP   Paraffin phase  CFPP                                          Ex.  (ppm)   (°C.)                                                                         (% by vol.)                                                                           Appearance                                                                            (°C.)                                                                        CP (°C.)                     ______________________________________                                        1    300     -26    100     dispersed                                                                             -25   -11                                 2    300     -25    100     dispersed                                                                             -24   -10                                 5    300     -25    100     dispersed                                                                             -25   -13                                 ______________________________________                                    

The measured values in Table 5 show that the novel copolymers have notonly a good CFPP-improving effect but also an excellent effect asparaffin dispersants, which is evident from the good agreement of theCFPP values (20% bottom phase) with the total CFPP values.

We claim:
 1. An ethylene-based copolymer which is suitable as a flowimprover for mineral oil middle distillates and is composed of:a') from50 to 95.5% by weight of ethylene, b') from 4 to 30% by weight of one ormore vinyl esters of C₂ -C₆ -monocarboxylic acids, c') from 0.5 to 20%by weight of one or more vinylimidazoles of the formula II ##STR5##wherein R⁴, R⁵ and R⁶ may be identical or different and are eachhydrogen or C₁ -C₆ -alkyl, or from 0.5 to 20% by weight of one or moreaminoalkyl vinyl ethers of the formula III

    R.sup.7 R.sup.8 N--A.sup.2 --O--CR.sup.9 ═CR.sup.10 R.sup.11(III)

where R⁷ and R⁸ are each C₁ -C₆ -alkyl R⁹, R¹⁰ and R¹¹ are each hydrogenor C₁ -C₆ -alkyl and A² is C₂ -C₆ -alkylene, and d') from 0 to 10% byweight of one or more monomers which are copolymerizable with themonomers a') to c').
 2. The copolymer as claimed in claim 1, whereinmonomer b') is vinyl acetate or vinyl propionate.
 3. The copolymer asclaimed in claim 1, wherein R⁴ to R⁶ of the vinylimidazole II are eachhydrogen.
 4. The copolymer as claimed in claim 2, wherein R⁴ to R⁶ ofthe vinylimidazole II are each hydrogen.
 5. The copolymer as claimed inclaim 1, wherein diethylaminoethyl vinyl ether is the aminoalkyl vinylether III.
 6. The copolymer as claimed in claim 2, whereindiethylaminoethyl vinyl ether is the aminoalkyl vinyl ether III.
 7. Amethod of improving the flow of mineral oil middle distillates,comprising:incorporating the copolymer of claim 1 into said middle oildistillates.
 8. The method of claim 7, wherein said copolymer has aweight average molecular weight of from 500 to 5,000.
 9. A mineral oilmiddle distillate containing an effective flow improving amount of thecopolymer of claim 1.